A method for enhancing oil recovery in huff-puff oil production of tight oil from a fractured horizontal well by an optimized reservoir pressure, washing the horizontal well by sand flushing, injecting water into the reservoir to increase the stratum pressure around the horizontal well, and stopping the water injection when the pressure retention level is 100% at end stage of the water injection period. The method for enhancing oil recovery in huff-puff oil production of tight oil from a fractured horizontal well enables the crude oil in the pores of the matrix in the tight reservoir rock developed by the natural fracture to be further recovered. Comprehensive utilization of stratum energy boost, and imbibition replacement between the injected water and the reservoir crude oil improves the single-well production to enhance the oil recovery of a tight oil reservoir.